This invention relates to humidifiers and more particularly to the electrode type steam generating humidifiers.
Such humidifiers in which a current is passed between spaced electrodes in a water-carrying vessel are well-known. The current causes heating of the water and subsequently generation of steam which is passed into the air space, the moisture content of which is to be controlled.
The magnitude of the current and hence the steam generating ability is dependent on the voltage applied to the electrodes, the size, shape and spacing of the electrodes, the depth of immersion of the electrodes and the conductivity and volume of the water. A serious problem which has been recognized is that the conductivity of a water supply can vary by as much as 10:1 depending on the geological conditions of the source and also the conductivity of a particular water supply can vary daily in the same range (10:1) depending on variables such as interconnections in the water main and switching and/or mixing of the sources and the season of the year. Because the design of an evaporator is dependent on the conductivity of the water in the vessel, it is necessary to ensure that the conductivity of the water in the vessel is maintained near the value for which the evaporator was designed or else tedious adjustments or adaptations of the evaporator will be necessary to accommodate different water conductivities.
Furthermore, because of the continual evaporation of water from the vessel, impurities from the water remain in the vessel and increase in concentration to the point where flushing of the vessel is necessary to maintain the contained water conductivity at the designed value and to reduce mineral build-up on the electrodes. If flushing is carried out merely on a time basis, the water may be flushed when its conductivity is below the designed value. In any event, the loss of hot water from the system during flushing is likely to exceed that necessary to maintain the conductivity at the designed value.
U.S. Pat. No. 3,937,920 issued on Feb. 10, 1976 to Plascon A.G. discloses a system which deals with these problems by arranging for the conductivity of the water in the vessel to be maintained at a value which is considerably higher than the average conductivity of typical water sources. As water is boiled off, the conductivity in the vessel gradually rises to the optimum designed value.
The magnitude of the current between the electrodes is measured continuously and the actual time taken for the current to drop between two predetermined value is compared with the calculated time required for the current to drop between those two values when the conductivity of the water is at the designed value. If the actual time measured is shorter, some of the water is flushed from the vessel, as this represents an unacceptably high conductivity.